And it is not clear how to drop/snap in both control modes(experimenting will not make it clear).

You are absolutely right -- this part of the R'n'D Android port is not "ready for prime time" yet.

The obvious solution would be to (optionally) draw the virtual control buttons over the game screen -- unfortunately, this currently does not work, because R'n'D really uses a (for example) 672x560 screen on the (usually) 16:9 or 16:10 screen of the Android smartphone or tablet, which is then scaled to fit the screen by SDL2. This means that the game can get touch events from the left and right part of the screen, but cannot draw to it. (See Eizzoux' screen shots, which show this quite well -- the GamePad buttons are also drawn to the black left/right areas, because this is a separate application which overlays the game it controls.)

So I can see two possible solutions for now: Use a logical screen resolution that matches the physical screen resolution (aspect ratio wise), or always use the pysical screen resolution (or aspect ratio) by adding black areas to the left and right, which can then be drawn to.

A solution which would work out of the box with the current implementation would be to display a help screen which shows how the virtual buttons are arranged on the screen (although this would not be available in-game), so one would at least know which part of the screen does what when touched.

A third solution I am thinking of is a third input method that does not use virtual buttons at all, but directly controls the player on the playfield, but it would also need some graphical explanation, of course, to know how it works. But it wouldn't require on-screen display of virtual buttons. But it's not implemented yet.

Last but not least: Eizzoux, thanks a lot for your very helpful recommendation of the "GamePad" app, your very good explanation how to use it, and the helpful screenshots that demonstrates how things work!